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SOCIETY OF AMERICA
173
TOPAZAND PHENACITE FROM BALDFACE MOUNTAIN,
CHATHAM, NEW HAMPSHIRE
MenraNo P. Brr-rrNcs.
INTRODUCTION
In the mineralogical collections at Harvard University there
are approximately two hundred crystals oI topaz and forty crystals
of phenacite from South Baldface Mountain, Chatham, Nbw
Hampshire. The specimenswere collected by E. C. Andrews
of Chatham about thirty or forty years ago and purchased from
him about 1910. Kunzl called attention to this occurrenceol topaz
and phenacite in 1890and Eaklez published a brief paper on the
topazin 1898. The phenacite has been studied crystallographically
by Farrington and Tillotsons and also by Schallerl
GEOLOGICALRELATIONS
The present writer has visited the pocket from which some
of the topaz and phenacite are reputed to have come. It is a very
irregular ellipsoid in shape, being about five feet along its greatest
axis. A detailed study of the mineralogy has not yet been made,
but the pegmatite is composed essentially of perthitic feldspar,
smoky quartz, and biotite. Apparently many of the topaz and
phenacite crystals found by Andrews were detached, Iying on the
floor of the pocket, or more commonly in the talus of the mountain
slopes. The phenacite was implanted on smoky qvartz, topaz, or
feldspar. The pocket mentioned is located on the east slope of
South Baldface Mountain, at about 2900 feet elevation; a number
of other pockets are found in the vicinity. The country rock is a
medium textured somewhat miarolitic alkaline biotite granite
exposed as an oval-shaped stock, the north-south axis of which is
a mile and a hali long. This stock is satellitic to the late Paleozoic
alkaline batholith of the White Mountains.
I Kunz,G. F. Gnusar,mPrucrousSroNnsor Nonrn Alaprrce,p. 100,1890.
2 Eakle, A. S. Topaz Crystals in the Mineralogical Collection of the United
States National Museum. Proc. [.1. S. National, Museum, pp. 361-369, 1898'
a Farrington, O. C. and Tillotson, E. W., Jr. Notes on Various Minerals in the
FiekL Columbi,an Museum Publirations, Geologi'cal'Series,
Museum Collection.
Volume 3, pp. 131-163, 1908.
{ Schaller, W. T. Phenacite from New Hampshire. Bulletin 49O, U ' S. G. S.,
pp, 53-54., l9ll.
Zeit. Kryst.,48, p. 554, 1910.
t74
TE E AM ERICAN M IN ERALOGIST
TOPAZ
DrscnrprroN oF TrrE r.oRMS. The topaz crystals vary in size
from the largest whose dimensions are nine by six centimeters
to those less than a centimeter in diameter. They are in general
of short or moderate prismatic development, and bounded at one
end by a cleavageplane. A number are however doubly terminated,
often with extreme distortion of the terminal faces. They are
clear and either colorlessor faintly pink, sometimes with a bluish
border. The ten crystals measured completely yielded the forms
of the following table. The letters and axes of Dana,s System
are used. The angles agreed on the whole very well with those
given in Goldschmidt's Winkeltabellen.
TearB I. Fonusor Topazlnou SournBelolecn Mouxraw,
c (001)
D (010).
m (rr0)l
I
M
r
g
G
X
1(
y
J
t
h
a
d
i
u
o
r
Often present, either as a narrow facet or occasionally as a broad face.
Not rare, but inconspicuous.
Always presentand one or both dominant in the prism zone,
e2ql
(230) Rare and narrow face.
(250)l
Observed,as narrow facets,but once.
ifgoi/
(065) Rare and narrow face.
(043) Commonand sometimesdominant brachvdome.
(08s))
Rare and narrow forms.
iossi/
(021) Usually the dominant brachydomeand a center of interesting zones.
(041). Common,sometimeslarge.
Q}3)l
Commonfaces,often well developed.
iZOll
(405) Seenbut once,
(223)l
(tll)l
All of thesepyramids are generallypresentwith variable development.
(221))
(241) Seenbut once.
NBw aNr RARE FoRMS. The unique feature of the topaz from
Baldface Mountain is a series of narrow pyramid faces grouped
about the brachydome f(021).
Their zonal relations are well
shown in the gnomonic projection, fig. 1, which contains also the
forms of Table 1. The form 2t (1.11.6) lies at the intersection of
the zone [112], which contains f and, u, and the zone [934], which
containX
s a n dg . O ( 2 . 1 8 . 9 ) ,I ( 2 . 2 4 . 7 1 ) a
, nd,g (2.30.13)
all lie in the zone [926]containingh and.(031) and at the intersections
with it of the threezones[012],[ll2], and [212]containing
JOUKNAL MINERALOGICAL
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Figure 1. Gnomonic Projection ol Topaz from Baldface Mtn.
respectively the forms f and o, J and m, and / and I' Although
these forms have complex indices, the fact that they are true
forms is demonstrated not only by the definite zonal relations
but also by the number of times they were observed and the
constancy of the angles. The form O(2'18'9) was noted sixteen
times; in ten of these cases the edges were so rounded that a
blurred and continuous signal resulted, but in six casesthe signal
was sufficiently good for accurate measurement and the readings
are noted in the accompanying table. The close-agreementof the
measured and calculated values emphasizesthe legitimacy of the
form. The form 2t (1'11'6) is nearly as well developed; in four
of the ten occurrencesthe signal was suficiently sharp for purposes
of calculation. The forms fi(2' 24' lI) and $(2'30'13) are not so
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TH E AM EKICAN MINERALOGIST
definite; both were found six times, but in only one casefor each
form was the face free from rounding. Nevertheless,the observed
and calculated angles are close. The appearanceof these narrow
f a c e sg r o u p e d a b o u t / ( 0 2 1i)s s h o w ni n f i g u r e4 . T h e f o r m 2 [ ( 1 .1 1 . 6 )
has been reported as uncertain by Biickings from the Fichtelgebirgesand also by Rosicky;6the other three forms have not been
reported.
Tanrn 2. ANcrus or. New am Renp Fonus oll Topez lnolr Ber,orecu Mrn.
Miller
Calculated
Indices
.b
p
a
+8
'I
(1.11.6)
S)
(2.18.e)
11 52
U
(2.24.11)
858
46 29
9 3l
o
(2.so.r3)
I
48 00
/JO
9" 45',
4lo 26'
9" 09' - 9
taa
Figure 2.
t l
ni
1n
t2 0 1 - 2 7
Topaz. Typical Baldface Habit.
5 Biicking, H. Neues Vorkommen
von Kalfeldspat, Turmalin, Apatit, und
Topas im Granit des Fichtelgebirges . Ber. SneckenbergischeNaturJor. Gesel.Frankfort, p. 748, 189O.
6 R.osickf,,Abh. Bdhm. Ak.,p.23, 1916.
JOURNAL MINERALOGICAL
SOCIETY OF AMERICA
Hesrr.
The topaz crystals fall generally into two types of
habit. The most common, illustrated by figure 2, is of rhombic
gection, rather short prismatic, with the base very subordinate,
ra dominant in the prism zone, and / the dominant brachydome.
Frequently I rather than m is dominant in the.prism zone. Sometimes X is the most prominent brachydome,as in the doubly terminated crystal in figure 3. The secondhabit, which has an equant
section with a broad basal plane, is seen on but few crystals.
Figure 4 is of this habit, but more modified than usual.
Figure 3.
Figure 4
.
Doubly Terminated Topaz from Baldface Mountain.
Baldface Topaz Showing Strong Development of the Base and the
Rare Pyramids around the Brachydome/.
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TEE AMERICAN MINERALOGIST
Etcnrxc. The prisms are often striated parallel to the c-axis.
Etching of all common forms is noted. fn some forms the brachydomes are more afiected, in other crystals the pyramids are most
strongly attacked. In general the etch figures on the orthodomes
and pyramids are more closely spaced and smaller than those on
the brachydomes, the resulting surface in the former case simulating ground glass.
PHBNACITE
The Baldface phenacite is always lenticular due to the dominance of the positive unit rhombohedron and the slight development of the prisms. Six of the forty phenacite crystals were
measured on the two-circle goniometer; on two of these crystals
both terminations were measured. Five other crystals were set
up for partial study. The prisms a(t2Q
and m(0T0) when
present occur as narrow faces; the prism fr(4150) is very rare.
The positive unit rhombohedron r(1011) is always conspicuous
and_usually the dominant form; the negative rhombohedron
d(0112) is usually prominent, occasionally surpassing in development the positive unit rhombohedron. The negatire rhombohedron p(0221) is often present as a narrow face between d and m.
Figure 5. Phenacitefrom Baldface Mountain.
The complementary second order rhombohedrons ! (1123 r)
and p{2LI3 l) are often prominent, occurring as rectangular faces
between r and d.. The secondorder rhombohedron ot (42231) occurs
as a small face and has been found only four times, twice on each
of two crystals. The crystals are arbitrarily set up so as to throw
this form onto the left hand boundary of the positive quadrant.
The complementary form o(2243 r) has not been found. The
JOURNAL MINERALOGICALSOCIETY OF AMERICA
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third order rhombohedrons are always inconspicuous. The
complementaryforms s(2131r) and sr (3121l) are found as narrow
faces in the positive quadrant between r and a. x(I322 r) and
n (1232 l) are in the negative qugdrant and inconspicuous. The
third order rhombohedron v1(3124 l), which occurs in the left
hand portion of the positive quadrant, was found but once, on
one of the crystals showing o1 (42231). The complementary from
vQfia r) has not been observed by the present writer, but Schallera
has reported it, and also one other form, A(1456l), not found on
these crystals. The typical lenticular habit and the tetartohedral
rhombohedral symmetry are shown in the accompanying figure 5.
Etching of the Baldface phenacite is common.